The present invention is directed to a portable diesel engine primer to assist starting an engine which has been overhauled, stored for a long period or out of diesel fuel. This apparatus is not a cold weather starting aid for diesel engines. The apparatus is a portable unit having an air pressurizable tank for a supply of diesel fuel which may be charged with fuel and pressurized to a predetermined air pressure depending upon the type of diesel engine to be started. The pressurized fuel is introduced to the engine through an engine cut-off valve connectable to the engine secondary fuel filter. The source of air to the tank may be from a service air charging connection such as found at most garages and filling stations. The tank is protected by an adjustable pop-off off valve which may be set to protect both the engine and the tank. The apparatus is portable and may be moved by service technicians manually about a service facility or put in a pickup truck and taken out in the field to the engine to be started.